The present invention relates to display devices and in particular, but not exclusively, to display devices incorporating liquid crystal display elements.
Colour sequential liquid crystal displays are known, such as those described in, for example, GB 2 172 733A, EP 0301715 and EP 0261896. In these arrangements, a complete field of one of the primary colours for display is written into the liquid crystal display (LCD) while the light sources for backlighting the display are switched off, i.e. the display is in darkness. The light source of the appropriate colour is then energised for a short period so as to display the colour concerned through those pixel elements of the LCD which have been set to their light transmissive state whilst the display is in its dark state. At the end of this short period of light source energisation a field of a second of the primary colours is written into the display whilst the display is held in its dark state, i.e. the light sources for backlighting the display are switched off. The lamp of the second primary colour is then energised for a short period to display the appropriate colour. The process is then repeated for the third primary colour and the eye of a viewer of the LCD integrates the three sequentially displayed colours, which is thereby perceived as a field of colour picture information.
Hence it can be seen that to provide a colour picture, the picture information for the whole display must be written three times per frame period, generally of 20 milliseconds duration, and arranging that, in time gaps between the writing operations, the appropriately coloured lamp is energised.
Typically, the three primary colours are used to build the colour picture for display and, hence, each frame period is divided into three time segments each of which is dedicated to a respective primary colour, and the time available for writing and illuminating respectively in each time segment is allocated, typically, in the ratio 3:1. Thus, in sequence, the first quarter of a frame period is dedicated to writing information of one colour, usually `red`, into the display and the following twelfth of the frame period is used to illuminate the display with light of that colour (red). The following quarters and twelfths of the frame period are used, respectively, to write and display the other two primary colours, usually in the order of `green` and then `blue`.
The constraint of illuminating the lamp of each colour for only one twelfth of each frame period severely limits the brightness of the display. Furthermore, in view of restraints on power dissipation and typical lamp response times, the situation cannot be readily improved by increasing lamp wattage, thereby merely causing the lamps to provide more light during their very brief periods of illumination.